linux-kernel - Re: [PATCH v4 4/4] i2c: i2c-qcom-geni: Enable i2c controller sharing between two subsystems

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Message-ID: <8508988c-a74b-4f65-8060-30a0cb5afa64@oss.qualcomm.com>
Date: Fri, 22 Nov 2024 14:42:56 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        konrad.dybcio@...aro.org, andersson@...nel.org, andi.shyti@...nel.org,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        conor+dt@...nel.org, agross@...nel.org, devicetree@...r.kernel.org,
        vkoul@...nel.org, linux@...blig.org, dan.carpenter@...aro.org,
        Frank.Li@....com, konradybcio@...nel.org, bryan.odonoghue@...aro.org,
        krzk+dt@...nel.org, robh@...nel.org
Cc: quic_vdadhani@...cinc.com
Subject: Re: [PATCH v4 4/4] i2c: i2c-qcom-geni: Enable i2c controller sharing
 between two subsystems

On 18.11.2024 6:45 AM, Mukesh Kumar Savaliya wrote:
> Thanks for the review konrad !
> 
> On 11/16/2024 12:58 AM, Konrad Dybcio wrote:
>> On 13.11.2024 5:14 PM, Mukesh Kumar Savaliya wrote:
>>> Add support to share I2C controller in multiprocessor system in a mutually
>>> exclusive way. Use "qcom,shared-se" flag in a particular i2c instance node
>>> if the usecase requires i2c controller to be shared.
>>
>> Can we read back some value from the registers to know whether such sharing
>> takes place?
> Actually, HW register doesn't provide such mechanism, it's add on feature if SE is programmed for GSI mode.

So it's more of an unwritten contract between subsystems.. okay

>>
>>> Sharing of I2C SE(Serial engine) is possible only for GSI mode as client
>>> from each processor can queue transfers over its own GPII Channel. For
>>> non GSI mode, we should force disable this feature even if set by user
>>> from DT by mistake.
>>
>> The DT is to be taken authoritatively
>>
> To clarify - Does it mean i should not have SW disable this feature OR override  ? And let it continue in non GSI mode even it's not going to work ?

If a configuration is invalid, you should return -EINVAL from probe,
with an appropriate error message.

>>>
>>> I2C driver just need to mark first_msg and last_msg flag to help indicate
>>> GPI driver to take lock and unlock TRE there by protecting from concurrent
>>> access from other EE or Subsystem.
>>>
>>> gpi_create_i2c_tre() function at gpi.c will take care of adding Lock and
>>> Unlock TRE for the respective transfer operations.
>>>
>>> Since the GPIOs are also shared between two SS, do not unconfigure them
>>> during runtime suspend. This will allow other SS to continue to transfer
>>> the data without any disturbance over the IO lines.
>>>
>>> For example, Assume an I2C EEPROM device connected with an I2C controller.
>>> Each client from ADSP and APPS processor can perform i2c transactions
>>> without any disturbance from each other.
>>>
>>> Signed-off-by: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
>>> ---
>>
>> [...]
>>
>>>       } else {
>>>           gi2c->gpi_mode = false;
>>> +
>>> +        /* Force disable shared SE case for non GSI mode */
>>> +        gi2c->se.shared_geni_se = false;
>>
>> Doing this silently sounds rather odd..
> we can have Some SW logging added ?

Normally such overrides mandate a warning/notice, but as I said above,
we should disallow such combinations altogether for sanity

Konrad